JP-A-H09-249328 discloses a configuration in which a drive gear driven by a motor is meshed with a gear attached to a feed roller shaft, thereby allowing the rotation of the motor to be transmitted to the feed roller shaft via the gear. At this time, a helical gear is employed as the gear to transmit rotational motions smoothly and prevent occurrence of noise.
In such an arrangement, to control the rotation of the feed roller shaft, a disc is attached to the feed roller shaft, and a sensor body for detecting the disc being rotated is attached to the frame. The disc is disposed to pass through a slit in the sensor body, so that the sensor body detects magnetically or optically the rotation of the disc in a non-contact manner.
However, when the helical gear transmits the rotation of the motor, a thrust force determined by the tilt angle of teeth of the helical gear is produced. This thrust force may move the disc in the direction of thrust of the feed roller shaft. Thus, the disc may contact with the sensor body and may be worn out or scratched. In such a case, detection of rotational motions may fail.